Enzymatic fuel cell

ABSTRACT

Provided is a battery comprising a first compartment, a second compartment and a barrier separating the first and second compartments, wherein the barrier comprises a proton transporting moiety.

The present invention relates to batteries, including fuel cells andre-chargeable fuel cells, for use in powering electrical devices.

Batteries such as fuel cells are useful for the direct conversion ofchemical energy into electrical energy. Fuel cells are typically made upof three chambers separated by two porous electrodes. A fuel chamberserves to introduce a fuel, typically hydrogen gas, which can begenerated in situ by “reforming” hydrocarbons such as methane withsteam, so that the hydrogen contacts H₂O at the first electrode, where,when a circuit is formed between the electrodes, a reaction producingelectrons and hydronium (H₃O⁺) ions is catalyzed.2H₂O+H₂

2H₃O⁺+2e⁻  (1)A central chamber can comprise an electrolyte. The central chamber actsto convey hydronium ions from the first electrode to the secondelectrode. The second electrode provides an interface with a recipientmolecule, typically oxygen, found in the third chamber. The recipientmolecule receives the electrons conveyed by the circuit.2H₃O⁺+1/2O₂+2e⁻

3H₂O  (2)

The electrolyte element of the fuel cell can be, for example, aconductive polymer material such as a hydrated polymer containingsulfonic acid groups on perfluoroethylene side chains on aperfluoroethylene backbone such as Nafion™ (du Pont de Nemours,Wilmington, Del.) or like polymers available from Dow Chemical Co.,Midland, Mich. Other electrolytes include alkaline solutions (such as 35wt %, 50 wt % or 85 wt % KOH), acid solutions (such as concentratedphosphoric acid), molten electrolytes (such as molten metal carbonate),and solid electrolytes (such as solid oxides such as yttria(Y₂O₃)-stabilized zirconia (ZrO₂)). Liquid electrolytes are oftenretained in a porous matrix. Such fuel cells are described, for example,in “Fuel Cells,” Kirk-Othmer Encyclopedia of Chemical Technology, FourthEdition, Vol. 11, pp. 1098-1121.

These types of fuel cells typically operate at temperatures from about80° C. to about 1,000° C. The shortcomings of the technology includeshort operational lifetimes due to catalyst poisoning from contaminants,high initial costs, and the practical restrictions on devices thatoperate at relatively high to extremely high temperatures.

The present invention provides a fuel cell technology that employsmolecules used in biological processes to create fuel cells that operateat moderate temperatures and without the presence of harsh chemicalsmaintained at high temperatures, which can lead to corrosion of the cellcomponents. While the fuel used in the fuel cells of the invention aremore complex, they are readily available and suitably priced for anumber of applications, such as power supplies for mobile computing ortelephone devices. It is anticipated that fuel cells of the inventioncan be configured such that a 300 cc cell has a capacity of as much as80 W·h—and thus can have more capacity than a comparably sized batteryfor a laptop computer—and that such cells could have still greatercapacity. Thus, it is believed that the fuel cells of the invention canbe used to increase capacity, and/or decrease size and/or weight.Moreover, the compact, inert energy sources of the invention can be usedto provide short duration electrical output. Since the materialsretained within the fuel cells are non-corrosive and typically nototherwise hazardous, it is practical to recharge the fuel cells withfuel, with the recharging done by the consumer or through a service suchas a mail order service.

Moreover, in certain aspects, the invention provides fuel cells that useactive transport of protons to increase sustainable efficiency. Fuelcells of the invention can also be electrically re-charged.

SUMMARY OF THE INVENTION

In one aspect, the invention provides a fuel cell comprising a firstcompartment, a second compartment and a barrier separating the first andsecond compartments, wherein the barrier comprises a proton transportingmoiety.

In another aspect, the invention provides a fuel cell a firstcompartment; a second compartment; a barrier separating the firstcompartment from the second compartment; a first electrode; a secondelectrode; a redox enzyme in the first compartment in communication withthe first electrode to receive electrons therefrom, the redox enzymeincorporated in a lipid composition; an electron carrier in the firstcompartment in chemical communication with the redox enzyme; and anelectron receiving composition in the second compartment in chemicalcommunication with the second electrode, wherein, in operation, anelectrical current flows along a conductive pathway formed between thefirst electrode and the second electrode.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 displays a perspective view of the interior of a fuel cell withthree chambers.

FIG. 2 illustrates a fuel cell exhibiting certain preferred aspects ofthe present invention.

FIGS. 3A, 3B and 3C illustrate a similar fuel cell withscavenger-containing segment.

FIGS. 4A and 4B show a top view of a fuel cell with two chambers.

FIG. 5A shows a top view of a fuel cell with two chambers, while FIG. 5Bshows a side view.

FIG. 6 shows a fuel cell where the fluids bathing the two electrodes aresegregated.

FIG. 7 shows a fuel cell with incorporated light regulation and asensor.

DEFINITIONS

The following terms shall have, for the purposes of this application,the respective meaning set forth below.

-   -   electron carrier: An electron carrier is a composition that        provides electrons in an enzymatic reaction. Electron carriers        include, without limitation, reduced nicotinamide adenine        dinucleotide (denoted NADH; oxidized form denoted NAD or NAD⁺),        reduced nicotinamide adenine dinucleotide phosphate (denoted        NADPH; oxidized form denoted NADP or NADP⁺), reduced        nicotinamide mononucleotide (NMNH; oxidized form NMN), reduced        flavin adenine dinucleotide (FADH₂; oxidized form FAD), reduced        flavin mononucleotide (FMNH₂; oxidized form FMN), reduced        coenzyme A, and the like. Electron carriers include proteins        with incorporated electron-donating prosthetic groups, such as        coenzyme A, protoporphyrin IX, vitamin B 12, and the like        Further electron carriers include glucose (oxidized form:        gluconic acid), alcohols (e.g., oxidized form: ethylaldehyde),        and the like. Preferably the electron carrier is present in a        concentration of 1 M or more, more preferably 1.5 M or more, yet        more preferably 2 M or more.    -   electron-receiving composition: An electron-receiving        composition receives the electrons conveyed to the cathode by        the fuel cell.    -   electron transfer mediator: An electron transfer mediator is a        composition which facilitates transfer to an electrode of        electrons released from an electron carrier.    -   redox enzyme: An redox enzyme is one that catalyzes the transfer        of electrons from an electron carrier to another composition, or        from another composition to the oxidized form of an electron        carrier. Examples of appropriate classes of redox enzymes        include: oxidases, dehydrogenases, reductases and        oxidoreductases. Additionally, other enzymes, will redox        catalysis as their secondary property could also be used e.g.,        superoxide dismutase.    -   composition. Composition refers to a molecule, compound, charged        species, salt, polymer, or other combination or mixture of        chemical entities.

DETAILED DESCRIPTION

FIG. 1 illustrates features of an exemplary battery such as a fuel cell10. The fuel cell 10 has a first chamber 1 containing an electroncarrier, with the textured background fill of the first chamber 1illustrating that the solution can be retained within a porous matrix(including a membrane). Second chamber 2 similarly contains anelectrolyte (and can be the same material as found in the first chamber)in a space, which space can also be filled with a retaining matrix,intervening between porous first electrode 4 and porous second electrode5. A face of second electrode 5 contacts the space of third chamber 3,into which an electron receiving molecule, typically a gaseous moleculesuch as oxygen, is introduced. First electrical contact 6 and secondelectrical contact 7 allow a circuit to be formed between the twoelectrodes.

The optional porous retaining matrix can help retain solution in, forexample, the second chamber 2 and minimize solution spillover into thethird chamber 3, thereby maintaining a surface area of contact betweenthe electron receiving molecule and the second electrode 5. In someembodiments, the aqueous liquid in the first chamber 1 and secondchamber 2 suspends non-dissolved reduced electron carrier, therebyincreasing the reservoir of reduced electron carrier available for useto supply electrons to the first electrode 4. In another example, wherethe chambers include a porous matrix, a saturated solution can beintroduced, and the temperature reduced to precipitate reduced electroncarrier within the pores of the matrix. Following precipitation, thesolution phase can be replaced with another concentrated solution,thereby increasing the amount of electron carrier, which electroncarrier is in both solid and solvated form.

It will be recognized that the second chamber can be made up of apolymer electrolyte, such as one of those described above.

The reaction that occurs at the first electrode can be exemplified withNADH as follows:H₂O+NADH

NAD⁺+H₃O⁺+2e⁻  (3)Preferred enzymes relay the electrons to mediators that convey theelectrons to the anode electrode. Thus, if the enzyme normally conveysthe electrons to reduce a small molecule, this small molecule ispreferably bypassed. The corresponding reaction at the second electrodeis:2H₃O⁺+1/2O₂+2e⁻

3H₂O  (2)Using reaction 2, preferably the bathing solution is buffered to accountfor the consumption of hydrogen ions, or hydrogen ion donating compoundsmust be supplied during operation of the fuel cell. This accounting forhydrogen ion consumption helps maintain the pH at a value that allows auseful amount of redox enzymatic activity. To avoid this issue, analternate electron receiving molecule with an appropriateoxidation/reduction potential can be used. For instance, periodic acidcan be used as follows:H₃O⁺+H₅IO₆+2e⁻

IO₃ ⁻+4H₂O  (4)The use of this reaction at the cathode results in a net production ofwater, which, if significant, can be dealt with, for example, byproviding for space for overflow liquid. Such alternative electronreceiving molecules are often solids at operating temperatures orsolutes in a carrier liquid, in which case the third chamber 3 should beadapted to carry such non-gaseous material. Where, as with periodicacid, the electron receiving molecule can damage the enzyme catalyzingthe electron releasing reaction, the second chamber 2 can have asegment, as illustrated as item 8 in fuel cell 10′ of FIG. 2, containinga scavenger for such electron receiving molecule.

In a preferred embodiment, the electrodes comprise metallizations oneach side of a non-conductive substrate. For example, in FIG. 3A themetallization on a first side of dielectric substrate 42 is the firstelectrode 44, while the metallization on the second side is the secondelectrode 45. Perforations 49 function as the conduit between the anodeand cathode of the fuel cell, as discussed further below. Theillustration of FIG. 3A, it will be recognized, is illustrative of therelative geometry of this embodiment. The thickness of dielectricsubstrate 42 is, for example, from 15 micrometer (μm) to 50 micrometer,or from 15 micrometer to 30 micrometer. The width of the perforationsis, for example, from 20 micrometer to 80 micrometer. Preferably,perforations comprise in excess of 50% of the area of any area of thedielectric substrate involved in transport between the chambers, such asfrom 50 to 75% of the area. In certain preferred embodiments, thedielectric substrate is glass or an polymer, such as polyvinyl acetateor soda lime silicate.

FIG. 3B illustrates the electrodes framed on a perforated substrate inmore detail. The perforations 49 together with the dielectric substrate42 provide a support for lipid bilayers (i.e., membranes) spanning theperforations. Such lipid bilayers can incorporate at least a firstenzyme or enzyme complex (hereafter “first enzyme”) 62 effective (i) tooxidize the reduced form of an electron carrier, and preferably (ii) totransport, in conjunction with the oxidation, protons from the fuel side41 to the product side 43 of the fuel cell 50. Preferably, the firstenzyme 62 is immobilized in the lipid bilayer with the appropriateorientation to allow access of the catalytic site for the oxidativereaction to the fuel side and asymmetric pumping of protons. However, asthe fuel is substantially isolated on the fuel side 41, an enzymeinserted into the lipid bilayer with the opposite orientation is withoutan energy source.

Examples of particularly preferred enzymes providing one or both of theoxidation/reduction and proton pumping functions include, for example,NADH dehydrogenase (e.g., from E. coli. Tran et al., “requirement forthe proton pumping NADH dehydrogenase I of Escherichia coli inrespiration of NADH to fumarate and its bioenergetic implications,” Eur.J. Biochem 244: 155, 1997), NADPH transhydrogenase, proton ATPase, andcytochrome oxidase and its various forms. Methods of isolating such anNADH dehydrogenase enzyme are described in detail, for example, in Braunet al., Biochemistry 37: 1861-1867, 1998; and Bergsma et al.,“Purification and characterization of NADH dehydrogenase from Bacillussubtilis,” Eur. J. Biochem. 128: 151-157, 1982. The lipid bilayer can beformed across the perforations 49 and enzyme incorporated therein by,for example, the methods described in detail in Niki et al., U.S. Pat.No. 4,541,908 (annealing cytochrome C to an electrode) and Persson etal., J. Electroanalytical Chem. 292: 115, 1990. Such methods cancomprise the steps of: making an appropriate solution of lipid andenzyme, where the enzyme may be supplied to the mixture in a solutionstabilized with a detergent; and, once an appropriate solution of lipidand enzyme is made, the perforated dielectric substrate is dipped intothe solution to form the enzyme-containing lipid bilayers. Sonication ordetergent dilution may be required to facilitate enzyme incorporationinto the bilayer. See, for example, Singer, Biochemical Pharmacology 31:527-534, 1982; Madden, “Current concepts in membrane proteinreconstitution,” Chem. Phys. Lipids 40: 207-222, 1986; Montal et al.,“Functional reassembly of membrane proteins in planar lipid bilayers,”Quart. Rev. Biophys. 14: 1-79, 1981; Helenius et al., “Asymmetric andsymmetric membrane reconstitution by detergent elimination,” Eur. J.Biochem 116: 27-31, 1981; Volumes on biomembranes (e.g. Fleischer andPacker (eds.)), in Methods in Enymology series, Academic Press.

Using enzymes having both the oxidation/reduction and proton pumpingfunctions, and which consume electron carrier, the acidification of thefuel side caused by the consumption of electron carrier is substantiallyoffset by the export of protons. Net proton pumping in conjunction withreduction of an electron carrier can exceed 2 protons per electrontransfer (e.g., up to 3 to 4 protons per electron transfer).Accordingly, in some embodiments care must be taken to buffer oraccommodate excess de-acidification on the fuel side or excessacidification of the product side. Alternatively, the rate of transportis adjusted by incorporating a mix of redox enzymes, some portion ofwhich enzymes do not exhibit coordinate proton transport. In someembodiments, care is taken especially on the fuel side to moderateproton export to match proton production. Acidification orde-acidification on one side or another of the fuel cell can also bemoderated by selecting or mixing redox enzymes to provide a desiredamount of proton production. Of course, proton export from the fuel sideis to a certain degree self-limiting, such that in some embodiments thetheoretical concern for excess pumping to the product side is of, atbest, limited consequence. For example, mitochondrial matrix proteinswhich oxidize electron carriers and transport protons operate to createa substantial pH gradient across the inner mitochondrial membrane, andare designed to operate as pumping creates a relatively high pH such aspH 8 or higher. (In some embodiments, however, care is taken to keep thepH in a range closer to pH 7.4, where many electron carriers such asNADH are more stable.) Irrespective of how perfectly proton productionis matched to proton consumption, the proton pumping provided by thisembodiment of the invention helps diminish loses in the electrontransfer rate due to a shortfall of protons on the product side.

In some embodiments, proton pumping is provided by a light-driven protonpump such as bacteriorhodopsin. Recombinant production ofbacteriorhodopsin is described, for example, in Nassal et al., J. Biol.Chem. 262: 9264-70, 1987. All trans retinal is associated withbacteriorhodopsin to provide the light-absorbing chromophore. Light topower this type of proton pump can be provided by electronic lightsources, such as LEDs, incorporated into the fuel cell and powered by a(i) portion of energy produced from the fuel cell, or (ii) a translucentportion of the fuel cell casing that allows light from room lighting orsunlight to impinge the lipid bilayer. For example, illustrated in FIG.7 is a fuel cell 400 in which light control devices 71 are incorporated.These light control devices 71 contain, for example, LEDs or liquidcrystal shutters. Liquid crystal shutters have a relatively opaque and arelatively translucent state and can be electronically switched betweenthe two states. An eternal light source, such as the light provided byroom lighting or sunlight can be regulated through the use of liquidcrystal shutters or other shuttering device. In some embodiments, thelight control devices are individually regulated or regulated in groupsto aid in regulating the amount of light conveyed to the proton pumpprotein. Preferably, the light control devices 71 have lenses to directthe light to focus primarily at the dielectric substrate 42,particularly those portions containing lipid bilayers incorporating theproton pumps. A monitoring device 72 can operate to monitor a conditionin the fuel cell, such as the pH or the concentration of electroncarrier, and relay information to a controller 73 which operates tomoderate an aspect of the operation of the fuel cell should monitoredvalues dictate such action. For example, the controller 73 can moderatethe level of light conveyed by the light control devices 71 dependingupon the pH of the fuel side 41. Note that in one embodiment an externallight source is allowed to energize the proton pump without the use ofany light-regulating devices.

In another embodiment, redox enzyme is deposited on or adjacent to thefirst electrode, while a proton transporter is incorporated into thelipid bilayers of the perforations.

In another embodiment, a second enzyme 63 is incorporated into the fuelcell, such as into the lipid bilayer or otherwise on the first electrodeor in the first chamber, to facilitate proton transport or generation inthe first chamber during recharge mode, thereby adding protons to thefuel side. The second enzyme can be the same as, or distinct from, theenzyme that transports protons during forward operation. An example ofthis second enzyme include transporting proteins with lower redoxpotential relative to, for example, NAD succinate dehydrogenase inconjunction with the CoQH₂-cyt c reductase complex. Also useful arelactate dehydrogenase and malate dehydrogenase, both enzymes isolatedfrom various sources available from Sigma Chemical Co., St. Louis, Mo.For example, bacteriorhodopsin can also be used with an orientationappropriate for this use in the recharge mode.

In some embodiments, the recharge mode operates to regenerate NADH, butdoes not reverse pump protons.

The perforations 49 are illustrated as openings. However, these can alsocomprise porous segments of the dielectric substrate 42. Alternatively,these can comprise membranes spanning the perforations 49 to support thelipid bilayer. Preferably, the perforations encompass a substantialportion of the surface area of the dielectric substrate, such as 50%.Preferably, enzyme density in the lipid bilayer is high, such as2×10¹²/mm².

The orientation of enzyme in the lipid bilayer can be random, witheffectiveness of proton pumping dictated by the asymmetric presence ofsubstrate such as protons and electron carrier. Alternatively,orientation is established for example by using antibodies to the enzymepresent on one side of the membrane during formation of the enzyme-lipidbilayer complex.

The perforations 49 and metallized surfaces (first electrode 44 andsecond electrode 45) of the dielectric substrate 42 can be constructed,for example, with masking and etching techniques of photolithographywell known in the art. Alternatively, the metallized surfaces(electrodes can be formed for example by (1) thin film depositionthrough a mask, (2) applying a blanket coat of metallization by thinfilm then photo-defining, selectively etching a pattern into themetallization, or (3) Photo-defining the metallization pattern directlywithout etching using a metal impregnated resist (DuPont Fodel process,see, Drozdyk et. al. “Photopatternable Conductor tapes for PDPapplications” Society for Information Display 1999 Digest, 1044-1047;Nebe et al., U.S. Pat. No. 5,049,480). In one embodiment, the dielectricsubstrate is a film. For example, the dielectric can be a porous filmthat is rendered non-permeable outside the “perforations” by themetallizations. The surfaces of the metal layers can be modified withother metals, for instance by electroplating. Such electroplatings canbe, for example, with chromium, gold, silver, platinum, palladium,nickel, mixtures thereof, or the like, preferably gold and platinum. Inaddition to metallized surfaces, the electrodes can be formed by otherappropriate conductive materials, which materials can be surfacemodified. For example, the electrodes can be formed of carbon(graphite), which can be applied to the dielectric substrate by electronbeam evaporation, chemical vapor deposition or pyrolysis. Preferably,surfaces to be metallized are solvent cleaned and oxygen plasma ashed.

As illustrated in FIG. 3C, electrical contact 54 connects the firstelectrode 44 to a prospective electrical circuit, while electricalcontact 55 connects the second electrode 45.

In one embodiment, the product side of the fuel cell is comprised of anaqueous liquid with dissolved oxygen. In an embodiment, at least aportion of the wall retaining such aqueous liquid is oxygen permeable,but sufficiently resists transmission of water vapor to allow a usefulproduct lifetime with the aqueous liquid retained in the fuel cell. Anexample of an appropriate polymeric wall material is an oxygen permeableplastic. In contrast, the fuel side is preferably constructed ofmaterial that resists the incursion of oxygen. The fuel cell can be madeanaerobic by flushing to purge oxygen with an inert gas such as nitrogenor helium. In some rechargeable embodiments, the electron-receivingcomposition is regenerated during recharging mode, thereby eliminatingor reducing the need for an outside supply of such electron-receivingcomposition.

The fuel cell of the invention can preferably be recharged by applyingan appropriate voltage to inject electrons into the fuel side to allowthe first enzyme to catalyze the reverse reaction. In particularlypreferred embodiments, the first enzyme has both the oxidation/reductionand proton pumping functions and operates to reverse pump protons fromthe product side to the fuel side during recharging. Thus, the reversepumping supplies the protons consumed in generating, for example, NADHfrom (i) NAD⁺ and (ii) the injected electrons and protons. Note that inreverse operation the injected electrons act first to reduce any oxygenresident in the fuel side, as this reaction is energetically favored.Once any such oxygen is consumed, the electrons can contribute toregenerating the reduced electron carrier.

The above discussion of the embodiments using proton transport focus onthe use of both faces of a substrate to provide the electrodes, therebyfacilitating a more immediate transfer of protons to the product sidewhere the protons are consumed in reducing the electron-receivingcomposition. However, it will be recognized that in this embodimentstructures such as a porous matrix can be interposed between the fuelside and the product side. Such an intervening structure can operate toprovide temperature shielding or scavenger molecules that protect, forexample, the enzymes from reactive compounds.

The fuel cell operates within a temperature range appropriate for theoperation of the redox enzyme. This temperature range typically varieswith the stability of the enzyme, and the source of the enzyme. Toincrease the appropriate temperature range, one can select theappropriate redox enzyme from a thermophilic organism, such as amicroorganism isolated from a volcanic vent or hot spring. Nonetheless,preferred temperatures of operation of at least the first electrode areabout 80° C. or less, preferably 60° C. or less, more preferably 40° C.or 30° C. or less. The porous matrix is, for example, made up of inertfibers such as asbestos, sintered materials such as sintered glass orbeads of inert material.

The first electrode (anode) can be coated with an electron transfermediator such as an organometallic compound which functions as asubstitute electron recipient for the biological substrate of the redoxenzyme. Similarly, the lipid bilayer of the embodiment of FIG. 3 orstructures adjacent to the bilayer can incorporate such electrontransfer mediators. Such organometallic compounds can include, withoutlimitation, dicyclopentadienyliron (C₁₀H₁₀Fe, ferrocene), availablealong with analogs that can be substituted, from Aldrich, Milwaukee,Wis., platinum on carbon, and palladium on carbon. Further examplesinclude ferredoxin molecules of appropriate oxidation/reductionpotential, such as the ferredoxin formed of rubredoxin and otherferredoxins available from Sigma Chemical. Other electron transfermediators include organic compounds such as quinone and relatedcompounds. The electron transfer mediator can be applied, for example,by screening or masked dip coating or sublimation. The first electrodecan be impregnated with the redox enzyme, which can be applied before orafter the electron transfer mediator. One way to assure the associationof the redox enzyme with the electrode is simply to incubate a solutionof the redox enzyme with electrode for sufficient time to allowassociations between the electrode and the enzyme, such as Van der Waalsassociations, to mature. Alternatively, a first binding moiety, such asbiotin or its binding complement avidin/streptavidin, can be attached tothe electrode and the enzyme bound to the first binding moiety throughan attached molecule of the binding complement.

The redox enzyme can comprise any number of enzymes that use an electroncarrier as a substrate, irrespective of whether the primary biologicallyrelevant direction of reaction is for the consumption or production ofsuch reduced electron carrier, since such reactions can be conducted inthe reverse direction. Examples of redox enzymes further include,without limitation, glucose oxidase (using NADH, available from severalsources, including number of types of this enzyme available from SigmaChemical), glucose-6-phosphate dehydrogenase (NADPH, BoehringerMannheim, Indianapolis, Ind.), 6-phosphogluconate dehydrogenase (NADPH,Boehringer Mannheim), malate dehydrogenase (NADH, Boehringer Mannheim),glyceraldehyde-3-phosphate dehydrogenase (NADH, Sigma, BoehringerMannheim), isocitrate dehydrogenase (NADH, Boehringer Mannheim; NADPH,Sigma), and α-ketoglutarate dehydrogenase complex (NADH, Sigma).

The redox enzyme can also be a transmembrane pump, such as a protonpump, that operates using an electron carrier as the energy source. Inthis case, enzyme can be associated with the electrode in the presenceof detergent and/or lipid carrier molecules which stabilize the activeconformation of the enzyme. As in other embodiments, an electrontransfer mediator can be used to increase the efficiency of electrontransfer to the electrode.

Associated electron carriers are readily available from commercialsuppliers such as Sigma and Boehringer Mannheim. The concentrations atwhich the reduced form of such electron carriers can be as high aspossible without disrupting the function of the redox enzyme. The saltand buffer conditions are designed based on, as a starting point, theample available knowledge of appropriate conditions for the redoxenzyme. Such enzyme conditions are typically available, for example,from suppliers of such enzymes.

As illustrated for the fuel cell 100 in FIG. 4A (top view), a sourcereservoir 111 can be provided to supply reduced electron carrier viaconduit 113, check-valve 112 and diffuser 114 to second chamber 102.Note that fuel cell 100 lacks a first chamber as this chamber oftenserves as a reservoir, which in fuel cell 100 is provided by sourcereservoir 111. Diffuser 115, conduit 116, and pump 117 provide thepathway and motive power for conveying spent liquid containing theelectron carrier (often merely having reduced effectiveness in poweringthe fuel cell) to an output reservoir 118. Fuel cell 100 further has afirst electrode 104, second electrode 105, third chamber 103, air pump121, air inlet 122, and air outlet 123. The various pumps can beoperated off of a battery, which can be recharged and regulated usingenergy from the fuel cell, or can come into operation after the fuelcell begins generating current. As illustrated in FIG. 4B, voltage orcurrent monitor M can monitor the performance the fuel cell in providingvoltage to the circuit comprising resister(s) R. Monitor M can relayinformation to the controller, which uses the information to regulateoperation of one or more of the pumps.

FIG. 5A illustrates a fuel cell 200 (top view) in which an acid/basereservoir 231 serves to supply a source of a material required toaccount for any material imbalances in the reaction equations at thefirst and second electrodes. The acid/base reservoir 231 is connectedvia conduit 232, first actuated valve 233, and diffuser 234 to a secondchamber 202. Liquid from source reservoir 211 is delivered via checkvalve 212A and second actuated valve 212B. In one example of operation,second actuated valve 212B is normally open, and first actuated valve233 is normally closed. These valve positions are reversed when thecontroller detects the need for fluid from acid/base reservoir 231(e.g., because of a signal received from a pH monitor) and operates pump117 (e.g., by use of a stepper motor) to draw fluid into the secondchamber 202.

It will be recognized that the pump and valve arrangements in FIGS. 4Athrough 5B are for illustration only, as numerous alternativearrangements will be recognized by those of ordinary skill. The plumbingof the fuel cell can be arranged to maintain a chamber less thanatmospheric pressure, for instance to help reduce fluid leakage throughvarious porous materials. The pores in various porous materials can beselected to allow such diffusion as is needed while minimizing fluidflow across the porous materials, such as bulk liquid flow into achamber designed to bring gas into contact with a porous electrode.

The chambers of fluid which the first and second electrodes contact canbe independent, as illustrated in FIG. 6. In fuel cell 300, the solutionbathing the first electrode (anode) is fed through conduit 313A, whilethat bathing the second electrode (cathode) is supplied through conduit313B. Flow is illustrated as regulated by pumps 317A and 317B. In theillustrated fuel cell, the bathing solutions are replenished as neededto account for the necessary imbalance in the chemistries occurring inthe segregated cells.

Cells can be stacked, and electrodes arranged in a number of ways toincrease the areas of contact between electrodes and reactants. Thesestacking and arranging geometries can be based on well-known geometriesused with conventional fuel cells.

It will be recognized that where the electron carrier has an appropriateelectrochemical potential relative to the electron-receiving molecule,the cell can be operated so that the oxidized form of the electroncarrier receives the electrons through an enzyme catalyzed event. Forexample, the electron carrier and the electron-receiving molecule canboth be of the class exemplified for electron carriers, but withdistinct electrochemical potentials. Thus, both the fuel side andproduct side reactions can be enzyme catalyzed. In fact, even with suchtraditional electron-receiving composition as oxygen, the product sidereaction can be enzyme catalyzed.

In one embodiment of the invention, the fuel cell does not incorporate aproton pump. Preferably, in this embodiment the redox enzyme isassociated with a lipid component, such as a composition containingphospholipid, steroids (such as sterols), glycolipids, sphinoglipids,triglyceride or other components typically incorporated intointracellular or external cellular membranes, while still beingsufficiently associated with the electrodes to convey electrons. Theenzyme is preferably incorporated into a lipid bilayer. The barrier canbe separating component such as is used in a typical fuel cell, whichpreferably conveys protons between the first and second chambers, thoughwithout requiring proton pumping.

The following examples further illustrate the present invention, but ofcourse, should not be construed as in any way limiting its scope.

EXAMPLE

The test apparatus consisted of a 5 ml reaction vessel which held thefuel and into which copper or other electrodes were dipped. Theelectrodes were in turn connected to a high impedance voltmeter for opencircuit voltage measurements or to a low impedance ammeter for shortcircuit current measurements. Various test configurations were employedto establish a baseline with which to measure performance of the cell.Testing was done by dipping electrodes in the fuel solution andmeasuring current and/or voltage as a function of time.

The reaction which drove the cell was the oxidation ofnicotinamide-adenine dinucleotide hydride (NADH) which is catalyzed bythe enzyme glucose oxidase (GOD) in the presence of glucose. Thisreaction yielded NAD⁺, a proton (H⁺) and 2 free electrons.H₂O+NADH=NAD⁺+H₃O⁺+2e⁻The reaction toke place at one electrode, which was a metallized plasticstrip coated with the enzyme GOD. This half-reaction was coupled throughan external circuit to the formation of water or hydrogen peroxide fromprotons, dissolved oxygen, and free electrons at the other electrode.

Fuels used were solutions of glucose, NADH or combinations thereof,distilled deionized water or a 50 mM solution of Tris™ 7.4 buffer. (NADHis most stable in a pH 7.4 environment.) Electrode materials were copper(as a reference) and metallized plastic strips coated with GOD (acommercially available product).

Test configurations employed as well as initial results were as follows:

Configuration 1:

-   -   Electrode 1: Copper    -   Electrode 2: Copper    -   Solution: 50 mM tris 7.4 buffer    -   Voltage: −7.5 mV    -   Current: 3 μA initially decaying to −2.2 μA within 3 minutes,        fairly constant thereafter.        Configuration 2:    -   Electrode 1: Copper    -   Electrode 2: GOD coated strip    -   Solution: 50 mM tris 7.4 buffer    -   Voltage: +350 mV    -   Current: >20 μA (+) initially decaying to +4 μA within 2        minutes, fairly constant thereafter.        Configuration 3:    -   Electrode 1: Copper    -   Electrode 2: Copper    -   Solution: 10 mM glucose in 50 mM tris 7.4 buffer    -   Voltage: −6.3 mVCurrent: −1.7 μA, fairly constant after initial        dropoff.        Configuration 4:    -   Electrode 1: Copper    -   Electrode 2: GOD coated strip    -   Solution: 10 mM glucose in 50 mM tris 7.4 buffer    -   Voltage: +350 mV    -   Current: >20 μA (+) initially decaying to −+2 μA within 2        minutes, fairly constant thereafter.        Configuration 5:    -   Electrode 1: Copper    -   Electrode 2: Copper    -   Solution: 10 mM glucose+10 mM NADH in 50 mM tris 7.4 buffer    -   Voltage: −290 mV slowly increasing to −320 after 4 minutes    -   Current: −25 μA, decaying to −21 μA after 2 minutes.        Configuration 6:    -   Electrode 1: Copper    -   Electrode 2: GOD coated strip    -   Solution: 10 mM glucose+10 mM NADH in 50 mM tris 7.4 buffer    -   Voltage: +500 mV decaying to +380 after 2 minutes    -   Current: >+30 μA, dropping rapidly to ˜+1 μA after 1 minute.

All publications and references, including but not limited to patentsand patent applications, cited in this specification are hereinincorporated by reference in their entirety as if each individualpublication or reference were specifically and individually indicated tobe incorporated by reference herein as being fully set forth. Any patentapplication to which this application claims priority is alsoincorporated by reference herein in its entirety in the manner describedabove for publications and references.

While this invention has been described with an emphasis upon preferredembodiments, it will be obvious to those of ordinary skill in the artthat variations in the preferred devices and methods may be used andthat it is intended that the invention may be practiced otherwise thanas specifically described herein. Accordingly, this invention includesall modifications encompassed within the spirit and scope of theinvention as defined by the claims that follow.

1. A battery comprising a first compartment, a second compartment and abarrier separating the first and second compartments, wherein thebarrier comprises a proton transporting moiety.
 2. A battery comprising:a first compartment; a second compartment; a barrier separating thefirst compartment from the second compartment; said barrier having aproton transporting moiety; a first electrode; a second electrode; aredox enzyme in the first compartment in communication with the firstelectrode to receive electrons therefrom; an electron carrier in thefirst compartment in chemical communication with the redox enzyme; andan electron receiving composition in the second compartment in chemicalcommunication with the second electrode, wherein, in operation, anelectrical current flows along a conductive pathway formed between thefirst electrode and the second electrode.
 3. The battery of claim 2,wherein the first electrode is further associated with an electrontransfer mediator that transfers electrons from the redox enzyme to thefirst electrode.
 4. The battery of claim 2, wherein the protontransporting protein comprises at least a portion of the redox enzyme.5. The battery of claim 2, adapted to operate at the first electrode ata temperature of about 60° C. or less.
 6. The battery of claim 2,further comprising a reservoir for supplying to the vicinity of at leastone of the electrodes a component consumed in the operation of thebattery and a pump for drawing such component to that vicinity.
 7. Thebattery of claim 6, further comprising a controller which receives dataon the operation of the battery and controls the pump in response to thedata.
 8. The battery of claim 2, wherein a light-driven proton pumpprotein comprises at least a portion of the proton transporting protein,and further comprising: a source of light for powering the light-drivenproton pump protein.
 9. The battery of claim 2, further incorporating inthe barrier a second protein, distinct from the first, adapted tofacilitate reverse proton pumping when the battery is operated inrecharge mode.
 10. A method of operating a battery with a firstcompartment and a second compartment comprising: enzymatically oxidizingan electron carrier and delivering the electrons to a first electrode inchemical communication with the first compartment; catalyzing thetransfer of protons from the first compartment to the secondcompartment; and reducing an electron receiving molecule with electrodesconveyed through a circuit from the first electrode to a secondelectrode located in the second compartment.
 11. The method of claim 10,wherein the catalytic transfer of protons occurs in conjunction with theenzymatic oxidation of the electron carrier.
 12. The method of claim 10,wherein at least a portion of the transfer of protons is driven by alight-driven proton pump protein, and the method further comprises:directing light to the light-driven proton pump.
 13. The method of claim12, further comprising monitoring the pH of the first compartment andcontrolling the amount of light directed to the light-driven proton pumpsuch that relatively more light is directed at lower pH values.
 14. Themethod of claim 10, further comprising: applying a voltage to theelectrodes of a polarity opposite that generated by the normal operationof the battery to recharge the battery.
 15. The method of claim 14,further comprising: enzymatically transporting protons from the secondchamber to the first chamber in connection with the applying therecharge voltage.
 16. The method of claim 15, wherein at least a portionof the enzymatic transport in recharge mode is accomplished by an enzymedistinct from an enzyme catalyzing the majority of proton transport in apower producing mode.
 17. A battery comprising: a first compartment; asecond compartment; a barrier separating the first compartment from thesecond compartment; a first electrode; a second electrode; a redoxenzyme in the first compartment in communication with the firstelectrode to receive electrons therefrom, the redox enzyme incorporatedin a lipid composition; an electron carrier in the first compartment inchemical communication with the redox enzyme; and an electron receivingcomposition in the second compartment in chemical communication with thesecond electrode, wherein, in operation, an electrical current flowsalong a conductive pathway formed between the first electrode and thesecond electrode.
 18. A method of operating a battery with a firstcompartment and a second compartment comprising: enzymaticallyoxidizing, with an enzyme incorporated into a lipid composition, anelectron carrier and delivering the electrons to a first electrode inchemical communication with the first compartment; and reducing anelectron receiving molecule with electrodes conveyed through a circuitfrom the first electrode to a second electrode located in the secondcompartment.